all co//2 in blood is in equilibrium, catalyzed by carbonic anhydrase (ca). this has prompted some investigators to consider treating ventilatory failure by using dialysis to remove hco//3** $minus$ . since there is at least 18 times more co//2 in the form of hco//3** $minus$ than dissolved co//2, theoretically, lower blood flows could be used than with current extracorporeal support with artificial membrane lungs. hco//3** $minus$ removal for ventilatory support has required alkalinization to compensate for the resulting acidosis and has been capable of removing 26 to 38 ml co//2/100 ml blood flow, compared to 14 ml co//2/100 ml for clinically employed silicone membrane lungs. we designed a hco//3** $minus$ removal system using recirculation of dialysate through a membrane lung to remove co//2, rather than alkalinization of blood, and removed 8.8 ml co//2/100 ml. adding ca improved this to 12.2 ml co//2/100 ml, but a conventional hollow fiber lung removed 30 ml co//2/100 ml. we conclude that the complexities of a carbon dioxide removal system may not be necessary with the advent of more efficient hollow fiber lungs. (author abstract) 15 refs